Liquid heavy hydrocarbon feedstocks are viscous liquid or semi-solid materials that are flowable at ambient conditions or can be made flowable at elevated temperature conditions. These materials are typically the residue from the processing of hydrocarbon materials such as crude oil.
For example, the first step in the refining of crude oil is normally a distillation to separate the complex mixture of hydrocarbons into fractions of differing volatility. A typical first-step distillation requires heating at atmospheric pressure to vaporize as much of the hydrocarbon content as possible without exceeding an actual temperature of about 650° F., since higher temperatures may lead to thermal decomposition. The fraction which is not distilled at atmospheric pressure is commonly referred to as “atmospheric petroleum residue”. The fraction may be further distilled under vacuum, such that an actual temperature of up to about 650° F. can vaporize even more material. The remaining undistillable liquid is referred to as “vacuum petroleum residue”. Both atmospheric petroleum residue and vacuum petroleum residue are considered liquid heavy hydrocarbon materials for the purposes of the present invention.
Liquid heavy hydrocarbon materials are in a relative sense low value materials, for example, as a fuel because of their high viscosity and low volatility, and increased concentration of impurities such as sulfur. For example, sulfur concentration in vacuum petroleum residue is typically at least about 2.5 times the concentration of sulfur in crude oil.
In the case of petroleum residues, the residue fraction typically constitutes more than 20% by mass of the starting crude oil, and in some cases more than 50% of the mass of the starting crude oil in the case of heavy crude oils, so there is high incentive to convert the residue to higher-value products such as, for example, lighter hydrocarbon liquids and gases.
Liquid heavy hydrocarbon materials may be subjected to destructive thermal decomposition to yield cracked liquid and gas, and still lower-value solid petroleum coke. The reactors for thermal decomposition are called cokers, and they may be fluidized bed reactors or stationary drums. Even though the resulting liquid products are higher-value, they still require much upgrading by reaction with hydrogen to be blended with other petroleum products.
Other outlets for liquid heavy hydrocarbon materials include blending with lower viscosity distillates to make residual fuel oil, or use as paving or roofing asphalts, which are also considered low-value uses.
Liquid heavy hydrocarbon materials may also be converted to low and medium BTU gases (syngas and methane-enriched synthesis gas) via catalytic and non-catalytic (thermal) gasification processes. The catalytic gasification (hydromethanation) of such materials in the presence of a catalyst source, hydrogen, carbon monoxide and steam at elevated temperatures and pressures to produce methane and other value-added gases is disclosed, for example, in U.S. Pat. No. 6,955,695, US2010/0071262A1, US2010/0076235A1, WO2010/033848A2 and WO2010/048493A2.
A need, however, remains for processes that can produce even higher value products, such as light olefins along with methane and other higher-value gaseous hydrocarbons, from liquid heavy hydrocarbon materials.
One such process is disclosed in U.S. Pat. No. 3,898,299, in which an atmospheric petroleum residue is first hydrogenated, then vacuum distilled into a liquid phase and a vacuum residue phase. The resulting lighter liquid phase is then thermally cracked (non-catalytically pyrolyzed) in the presence of steam to generate olefins. This process, however, only seems to utilize the lighter portions of the atmospheric petroleum residue, leaving significant amounts of additional residue material.
A catalytic process for upgrading liquid heavy hydrocarbon materials is disclosed in U.S. Pat. No. 3,816,298, but the disclosed process is focused on intermediate molecular weight liquid products and not lower molecular weight gaseous products. Specifically, the disclosed process converts a liquid heavy hydrocarbon material into a sulfur-reduced “normally liquid hydrocarbon product” (having an atmospheric boiling point of greater than 70° F.) and a hydrogen-containing gas by contacting the material with hydrogen and a carbon oxide-containing gas, at a pressure above 150 psig and a temperature between about 700° F. and 1100° F., in a first reaction zone containing a supported alkali metal catalyst. A solid material (coke) is also produced, which deposits on the supported alkali metal catalyst. A portion of the supported alkali metal catalyst is then fed to a second reaction zone where is it contacted with steam and optionally oxygen at a pressure above 150 psig and a temperature above 1200° F. to consume the deposited carbon, thereby regenerating the supported catalyst and producing hydrogen, carbon oxide-containing gas and heat energy for the first reaction zone. The hot regenerated support is also fed back into the first reaction zone. The first reaction zone of this process is thus essentially a coker unit, and the second reaction zone is essentially a gasification unit. The desired liquid products from this process include, for example, gasoline, heating oil and gas oil cuts. While there appear to be unsaturated compounds in the liquid product, it is actually a stated benefit of the disclosed process to reduce unsaturated components as they are detrimental, for example, in gasoline products. There is also no disclosure of the production of light olefins such as ethylene and propylene.
Several references also disclose the production of olefins from various residue feedstocks including, for example, U.S. Pat. No. 4,975,181, U.S. Pat. No. 4,980,053, U.S. Pat. No. 6,179,993, U.S. Pat. No. 6,303,842, WO2007/149917A1 and other disclosures cited therein. Generally, in these disclosures, the petroleum reside feedstock is contacted with a fluidized bed of heated solids and optionally a catalyst component (which may be the same or a separate component from the heated solids) at elevated temperatures and short contact times. A vapor phase is produced with light olefins and other light hydrocarbons, and coke is deposited on the heated particles. The coke-coated particles are regenerated and heated typically by burning off the coke. Catalysts are typically acidic components such as refractory metal oxides and aluminates, zeolites and spent fluid catalytic cracking catalysts, vanadium rich flue fines, spent bauxite and mixtures.
Notwithstanding the existing processes, a need still remains for additional processes for converting lower-value liquid heavy hydrocarbon materials into higher-value gaseous product mixes including light olefins and alkanes.